1. Technical Field
The present invention relates to a system, and process for use thereof, for inspecting wafers and other semiconductor substrates, and specifically for inspecting three dimensional (3D) features thereon such as bumps. Specifically, the present invention relates to a confocal optical system for inspecting bumps and other 3D features on wafers or like substrates, and a process of using such system.
2. Background Information
Over the past several decades, the semiconductor has exponentially grown in use and popularity. The semiconductor has in effect revolutionized society by introducing computers, electronic advances, and generally revolutionizing many previously difficult, expensive and/or time consuming mechanical processes into simplistic and quick electronic processes. This boom in semiconductors has been fueled by an insatiable desire by business and individuals for computers and electronics, and more particularly, faster, more advanced computers and electronics whether it be on an assembly line, on test equipment in a lab, on the personal computer at one""s desk, or in the home via electronics and toys.
The manufacturers of semiconductors have made vast improvements in end product quality, speed and performance as well as in manufacturing process quality, speed and performance. However, there continues to be demand for faster, more reliable and higher performing semiconductors.
One process that has evolved over the past decade plus is the semiconductor inspection process. The merit in inspecting semiconductors throughout the manufacturing process is obvious in that bad wafers may be removed at the various steps rather than processed to completion only to find out a defect exists either by end inspection or by failure during use. In the beginning, wafers and like substrates were manually inspected such as by humans using microscopes. As the process has evolved, many different systems, devices, apparatus, and methods have been developed to automate this process such as the method developed by August Technology and disclosed in U.S. patent application Ser. No. 09/352,564. Many of these automated inspection systems, devices, apparatus, and methods focus on two dimensional inspection, that is inspection of wafers or substrates that are substantially or mostly planar in nature.
One rapidly growing area in the semiconductor industry is the use of bumps or other three dimensional (3D) features that protrude outward from the wafer or substrate. The manufacturers, processors, and users of such wafers or like substrates having bumps or other three dimensional desire to inspect these wafers or like substrates in the same or similar manner to the two dimensional substrates. However, many obstacles exist as the significant height of bumps or the like causes focusing problems, shadowing problems, and just general depth perception problems. Many of the current systems, devices, apparatus, and methods are either completely insufficient to handle these problems or cannot satisfy the speed, accuracy, and other requirements.
The inspecting of semiconductors or like substrates, and specifically the inspection of three dimensional features, such as bumps, on their surface is accomplished by the present invention, which is a confocal sensor system to improve depth response by eliminating out of focus light thereby resulting in the sensor producing a signal only when the surface being inspected is in a narrow focal range. The result is an accurate height determination for a given point or area being inspected such that the cumulation of a plurality of height determinations from use of the confocal sensor system across a large surface allows the user to determine the topography thereof.
In sum, this system and process creates multiple parallel confocal optical paths along a line whereby the out of focus light is eliminated by placing an aperture at a plane which is a conjugate focal plane to the surface of the sample. The result is that the sensor produces a signal only when the sample surface is in a narrow focal range.